Thermal processing of silicon wafers is important for manufacturing modern microelectronics devices. Such processes, including silicide formation, implant anneals, oxidation, diffusion drive-in and chemical vapor deposition (CVD), may be performed using conventional low temperature thermal processing techniques. In contrast, some dopant activation processes are performed at substantially higher temperatures for relatively short durations of time. Such high temperature, short duration thermal processes are often called rapid thermal processes (RTP) or spike anneals. Many microelectronics circuits require feature sizes smaller than one micron and junction depths less than a few hundred angstroms. In order to limit both the lateral and downward diffusion of dopants, as well as to provide a greater degree of control during processing, it is desirable to minimize the duration of high temperature processing.
One approach for minimizing processing time utilizes a heat treatment apparatus such as a single-wafer RTP system. Single-wafer rapid thermal processing of semiconductor wafers provides a technique for fabrication of very-large-scale-integrated (VLSI) and ultra-large-scale-integrated (ULSI) electronic devices. There are several challenges, however, to meeting the thermal requirements of rapid thermal processing. For example, fast rates of change of wafer temperature are typically desired, as well as temperature uniformity across the wafer during the temperature changes.
One significant performance limitation of conventional RTP systems (e.g., in terms of thermal budget or the time the wafer spends above about 950 C) is rapidly cooling the wafer. Current systems typically rely almost exclusively on radiation cooling, which at 1000 C has a maximum heat transfer coefficient (HTC) of only about 22.7 mW/cm2C. In order to improve this performance, gas conduction cooling is needed. A challenge with gas conduction cooling is cooling uniformity across the wafer. In addition, for a spike anneal, one needs to turn-on the cooling gas conduction very quickly once the spike temperature is reached.
Thus there is a need in the art for the ability to readily adjust the wafer temperature during processing as well as provide temperature uniformity thereacross.